The problem isn't just Trump, it's the center of the GOP.
In 2008, Tancredo staked out the anti-Immigrant/Amnesty territory, got less than 1% of the vote and was dead before Iowa.
Trump seems to be happy to stake out this territory and he's doing a lot better.
Probably because the Cleetus Rank and File needs someone to blame, and they can't bring themselves to blame the One-Percenters.